Radial diffusion compressors having reduced rotor exits



Nov. 11, 1958 E. A. STALKER 2,859,909

RADIAL DIFFUSION COMPRESSORS HAVING REDUCED ROTOR EXITS Filed Jan. 51, 1952 IN VEN TOR.

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| F H4-L2e- RADIAL DIFFUSION COMPRESSORS HAVING REDUCED RDTOR EXITS Edward A. Stalker, Bay City, Mich. 7 Application January 31, 1952, Serial No. 269,239 Claims. (Cl. 230-120) This invention relates to axial flow compressors and particularly to the type wherein the diffusion of the fluid flow is radial. I

In my U. S. Patent application Serial No. 34,174 filed June 21, 1948, now Patent No. 2,785,849, and entitled Compressor Employing Radial Diffusion, I have disclosed a type of axial flow compressor which I have called a radial diffusion compressor because the fluid is diffused radially to effect a pressure rise in the rotor. The fluid is discharged from each rotor passage in a backward direction, that is with respect to the direction of rotation, and the radial depth of each-rotor passage at exit is greater than depths at upstream sections of each passage.

In the subject invention each passage of the rotor increases in radial depth and cross sectional area along a substantial portion of the passage length and then decreases in radial depth While retaining substantially the same cross sectional area.

Accordingly an object of'this invention is to provide a radial diffusion compressor whose radial diffusion rotor flow passages are characterized near their exits by a reduction in radial depth.

Another object is to provide a radial diffusion compressor rotor wherein each flow passage is curved along its aft portion and the radial depth is decreased therealong.

The above objects are accomplished by the means illustrated in the accompanying drawings in which- Fig. 1 is a rear view of the compressor of this invention;

Fig. 2 is an axial section of the compressor of Fig. 1;

Fig. 3 is a fragmentary development of the blading of the compressor rotor;

Fig. 4 is a front view of the compressor rotor; and

Fig. 5 is a fragmentary development of the blading of the stator.

Referring to the drawings the compressor is indicated generally as having the inlet 6 and exit 7. The compressor is comprised of the bladed rotor 12 mounted for rotation in the case portion 16 of the compressor case, and the stator is comprised of the cases 18 and 19 and blades 17.

The blades of the rotor are 20, spaced peripherally about the hub structure 21 and defining a plurality of flow passages 22. As shown, the hub structure has a substantial diameter in relation to the radial extent of the blades and is substantially coextensive in axial length therewith. The blades increase in radial depth rearward, that is in the direction of flow, along the forward portion 24 and then decrease in radial depth along the aft portion 26. The case fits closely to the tips of the blades and the portion of the case forwardly of and adjacent the exits of the flow passages extends in the same general direction as the axis of rotation, as. shown in Fig. 2.

The cross sectional areas of each flow passage 22 increase along the forward portions and then remain substantially constant along the rear portions. The curvature of the blades along the rear portion of each passage causes an increase in width of the passages and this is offset by the decrease in radial depth to keep the cross sectional areas substantially constant along the curved portions of the blades.

In order to induce the fluid in each rotor passage to fol rates Patent 0 ice low the curved portions of the blades without separation it is important that the flow does not have to proceed against an increasing static pressure. If the flow passage does not increase in cross sectional area substantially,'the static pressure will not increase substantially. Consequently the turning of the flow will be effected efiiciently.

When the radial depth is decreased while maintaining the cross sectional area the fluid pressure and mass flow are unaffected and the distribution of velocity and static pressure rise become more constant at all points of the radial depth of each passage.

In some instances it may be desirable to have the crosssectional areas decrease somewhat along the rear portions 26 of the passages so that the flow is somewhat accelerated while making the turns along the curved blades. Preferably the decrease in area along the rear portion of the passage is from 5 to 20 percent.

In the forward portion 24 of each passage the fluid.

flow is diffused with a large increase in static pressure. In the rear portion the static pressure is retained and the fluid is turned for the purpose of increasing the absolute velocity C of the fluid leaving the rotor as shown in Fig. 3. The peripheral velocity component is U and the axial velocity component is C. The dynamic pressure due to C is converted to static pressure in the stator and thereby added to the static pressure produced in the rotor.

The stator receives the flow of fluid from the rotor and directs it chiefly axially by means of the blades 17 spaced peripherally about the case.

As shown particularly in Fig. 3 each blade has sections of substantially parallel sides which facilitate fabrication from sheet metal. The blades are set at positive angles of incidence 0 as shown in Fig. 3 referred to the plane of rotation. The rear portion of each blade is curved chordwise toward the direction of rotation increasing the cross sectional width of each passage between adjacent blades.

The use of parallel-sided blade sections facilitates giving the leading edge and trailing edge portions fair contours, preferably a sharp trailing edge and a radiused leading edge which may be of very small radius. These sections also facilitate operation at high speed with large mass flow per second and high efficiency. This high efficiency is in part due also to the close spacing of the blades such that the leading edge of afollowing blade of a pair is further forward chordwise than the midpoint of the adjacent leading blade of the pair.

The rotor 12 is supported in bearings 40 and 42 by shafts 44 and 4.6 respectively.

The rotor passages are preferably expanded in cross sectional area along the forward portion 24 in the ratio of from 1.25 to 2.0. That is the cross sectional area of a passage at the rear end of its front portion is from 1.25 to 2.0 times the cross sectional area at the inlet although ratios as high as 4 are practical, particularly at low speeds where the change in density of the pumped fluid is small.

The axial length of the rotor may be of the order of the maximum radial depth of the passages.

An axial flow compressor is characterized by having the leading and trailing edges of its rotor blades extending radially. Thus the passages between the blades extend in the general axial direction from an inlet at the front of the rotor to an exit at the rear of the rotor for discharging fluid rearward in the general axial direction.

It will now be clear that the invention provides for much larger pressure rises than that achieved by the diffusion in the rotor passages. The additional pressure is produced by the additional whirl given to the fluid by the forward curved blades. Accompanying the gain in pressure there is achieved a more desirable velocity distribution across each rotor passage exit because there is less difference in peripheral velocity between the inner and outer walls of each rotor passage. Furthermore all the fluid leaving the rotor exits receives a greater peripheral velocity by having the hub diameter increased which of course raises the maximum pressure achieved.

The machine of this invention is useful in pumping all typesof fluid.

I claim:

1. In combination in an axial flow compressor, a bladed rotor comprising a rotatable hub structure and a plurality of axial flow blades carried thereon spaced peripherally thereabout defining a plurality of axial flow passages between said blades with inlets and exists respectively at the front and rear ends of said structure, said-hub structure being substantially coextensive in axial length with said blades and having a substantial diameter in relation to the radial extent of said blades, each said flow passage including a forward portion succeeded by a rearward portion, each said blade being set at a positive angle of incidence and having the rear portion thereof curved along the general axial direction to impart a whirl to the fluid resulting in additional pressure, the passages having substantially uniform widths over the forward portions thereof and having increasing widths over said curved rearward portions thereof, and a case enclosing said rotor and fitting closely to the tips of said blades and bounding said passages, forward portions of said case and said hub structure diverging one relative to the other and in cooperation with said blades providing said flow passages with cross sectional areas which increase rearward therealong to expand the flow in said forward portions, the rearward portions of said case and said hub converging one relative to the other in the rearward direction such as to offset the effect of said curved rear portions of said blades and to avoid increase in the cross sectional areas of said flow passages in the rearward portions thereof.

2. In combination in an axial flow pumping machine for increasing the pressure of a fluid, a case, a hub structure mounted in said case for rotation about an axis, and a plurality of axial flow blades carried on said hub structure spaced peripherally thereabout, said hub structure having a substantial diameter in relation to the radial extent of the blades and being substantially coextensive in axial length therewith, said blades having a plurality of axial flow passages therebetween with exits facing in the general axial direction, each said passage having increasing cross sectional areas along the forward portions thereof, the rearward portion of said hub struc ture increasing in diameter rearward therealong reducing the radial depth of each said passage along the rear portion thereof in cooperation with said case, said blades being set at a positive angle of incidence and having their aft portions curved chordwise toward the direction of rotation, said flow passages having increasing cross sectional widths along the rearward portions thereof, the cross sectional area at the exit of each said passage being greater than at the inlet thereof, said reduction in radial depth of the rear portions of said passages cooperating with the increased width thereof to avoid increase in the cross sectional areas of said rear passage portions.

3. In combination in an axial flow pumping machine for increasing the pressure of a fluid, a case, a hub structure mounted in said case for rotation about an axis, and a plurality of axial flow blades carried on said hub structure spaced peripherally thereabout, said'hub structure having a substantial diameter in relation to the radial extent of the blades and being substantially coextensive in axial-length therewith, said blades defining a plurality of axial flow passages therebetween with inlets and exits facing in the general axial direction, the forward portions of said case and said hub structure in cooperation with said blades having such shape that said flow passages have increasing cross sectional areas along the forward portions thereof, the rearward portion of said hub structure and said case converging rearward therealong reducing the radial depth of each said passage along the rear portion thereof, said blades being set at a positive angle of incidence and having their rear portions curved chordwise toward the direction'of rotation, said curved rear blade portions and said converging hub and case cooperating to provide decreasing cross sectional areas in said flow passages over the rearward portions thereof, the cross sectional area at the exit of each said passage being greater than at the inlet thereof.

4. In combination in an axial flow pumping machine for increasing the pressure of a fluid, acase having an increasing diameter over the forward portion thereof and a generally constant diameter over the rear portion thereof, a hub structure mounted in said case for rotation about an axis, and a plurality of axial flow blades carried on said hub structure spaced peripherally thereabout, said hub structure having a substantial diameter in relation to the radial extent of the blades and being substantially coextensive in axial length therewith, said blades defining a plurality of axial flow passages therebetween with exits facing in the general axial direction, each said passage having increasing cross sectional areas along the forward portions thereof to expand the flow radially in said forward portions of said flow passages, the rear portion of said hub structure increasing in diameter providing a smoothly curved rim surface of sinuous shape rearward therealong reducing the radial depth of each said passage along the rear portion thereof in cooperation with said case to restrict the flow radially along the rear portion of said flow passages, each said blade being set at a positive angle of incidence, the rear portions of said blades being curved chordwise toward the direction of rotation, said curved rear blade portions and said reduced radial depths of the rearward portions of said flow passages cooperating to avoid increase in the cross sectional areas of the rearward portions of the flow passages, the exits of said flow passages extending in the same general direction as the axis of rotation, the cross sectional area at the exit of each said passage being greater than at the inlet thereof.

5. In combination in an axial flow pumping machine for increasing the pressure of a fluid, a case, a hub structure mounted in said case for rotation about an axis, and a plurality of axial flow blades carried on said hub structure spaced peripherally thereabout, said hub structure having a substantial diameter in relation to the radial extent of the blades and being substantially coextensive in axial length therewith, said blades defining a plurality of axial flow passages therebetween with inlets and exits facing in the general axial direction, the forward portions of said case and said hub structure in cooperation with said blades having such shape that said flow passages have increasing cross sectional areas along the forward portions thereof, the rearward portion of said hub structure and said case converging rearward therealong reducing the radial depth of each said passage along the rear portion thereof, said blades being set at a positive angle of incidence and having their rear portions curved chordwise toward the direction of rotation, said curved rear blade portions and said converging hub and case cooperating to provide decreasing cross sectional areas in said flow passages over the rearward portions thereof, the cross sectional area and radial depth at the exit of each said passage being less than the maximum cross sectional area and radial depth of each said passage intermediate the inlet and the exit thereof to facilitate the turning of said flow by said blades.

References Cited in the file of this patent UNITED STATES PATENTS 1,086,754 Curtis Feb. 10, 1914 1,153,872 Matsler Sept. 14, 1915 2,398,203 Browne Apr. 9, 1946 2,469,125 Meisser May 3, 1949 2,628,768 Kantrowitz Feb. 17, 1953 2,663,493 Keast Dec. 22, 1953 

